This invention relates to a transmission system for a marine drive.
In a conventional marine drive, including an engine and a propulsion unit, the engine is directly and mechanically connected to the propeller through a gear box. As a result, the speed of the propeller is directly proportional to the speed of the engine in a ratio established by the gears of the gear box.
It has been recognized that the usual selection of marine drive characteristics provides unsatisfactory boat performance at low-speed operation, such as for trolling or docking. Mechanisms for improving the low-speed performance of a boat are disclosed in copending patent applications Ser. No. 07/255,618 filed Oct. 11, 1988 and 07/118,862 filed Nov. 9, 1987, now U.S. Pat. No. 4,820,209. The former application provides a fluid coupling apparatus in connection with a series of stationary variable position vanes disposed between the pump and turbine components of the fluid coupling. The vanes are movable so as to govern the direction of impingement of fluid on the turbine component of the fluid coupling. The position of the vanes governs the amount of power transferred from the fluid pump to the turbine, as well as the direction of rotation of the turbine. The latter patent discloses a fluid coupling structure including a fluid pump, a forward driven turbine and a reverse, or reaction, driven turbine. The forward and reaction turbines are connected to concentrically extending shafts. Through a series of gears, clutches and brakes, the forward and reverse turbine shafts drive an output shaft in either a first or second rotational direction, for propelling the boat either in a forward or reverse direction.
The present invention is also directed to a structure for providing improved low-speed and variable speed operation of a boat. A fluid coupling is provided between the marine drive engine and the gear box to which the propeller is connected. The fluid coupling includes a rotatable fluid pump connected to the engine and rotatable in response to rotation of the engine crankshaft. A rotatable forward turbine is adapted to be driven by the fluid pump, and a rotatable reverse turbine is also adapted to be driven by the fluid pump. The forward and reverse turbines preferably are driven in the same rotational direction. A rotatable output means, such as an output shaft, is drivingly connectible to the forward and reverse turbines. A selective engagement means selectively engages the forward and reverse turbines with the output shaft for selectively imparting rotation to the output shaft in either a first or second rotational direction. The reverse turbine is preferably disposed between the fluid pump and the forward turbine, and includes a plurality of vanes which are movable so as to govern the amount of power transferred from the fluid pump to the reverse turbine and the forward turbine. In one embodiment, counter-rotation means is provided between the reverse turbine and the output shaft so that, when the reverse turbine is engaged with the output shaft, the output shaft is driven in a rotational direction opposite its direction of rotation when engaged with the forward turbine. The counterrotation means preferably comprises a planetary gearset including a ring gear to which the reverse turbine is mounted, a sun gear mounted at its center to the output shaft, and two or more planet gears disposed between the sun gear and the ring gear. A substantially cylindrical rotatable carrier is mounted concentrically to the output shaft along at least a portion of its length. The carrier has mounting means at one end pivotably connected to the planet gears. A brake mechanism is engageable with the carrier for selectively maintaining the carrier stationary, and a clutch mechanism is disposed between the carrier and the output shaft for selectively coupling the output shaft to the carrier. A one way clutch is disposed between the forward turbine and the output shaft for ensuring that the forward turbine can only transfer power to the output shaft in one direction of rotation. A lock-up clutch is provided for directly mechanically coupling the output shaft to the fluid pump, so as to bypass the effect of the fluid coupling in response to certain predetermined operating conditions.
With the above described construction, the brake mechanism and the clutch mechanism can be selectively engaged to prevent rotation of the output shaft, or to provide rotation of the output shaft in either a first or second direction of rotation.